Hydroxylamine derivatives are cyclized with high stereoselectivity to give several classes of biologically interesting molecules such as the analogs of aminosugar and nucleoside. For example, high stereoselectivity was observed in the cycloaddition of hydroxylamine derivatives to acyclic ?, ?-unsaturated esters. The adducts were subsequently cyclized under mild conditions to afford a single isomer of isoxazolidin-5-ones which was easily converted to acetate-protected isoxazolidin-5-ols. The coupling of these intermediates and nucleoside bases gave ?-isoxazolidinyl nucleosides with high cis selectivity which has rarely been observed in the nonmetal-chelated cases of 2-deoxyfuranosyl coupling reactions. EI-MS, FAB-MS and exact mass measurements have been used to characterize these products.